U.S. Pat. No. 4,103,753 (J. W. Holdeman) describes a power transfer device of a type which is suited for use as a torque transfer case in an automotive vehicle, where such a device serves to transmit torque from an engine or prime mover to a plurality of drive axles to thereby drive front and rear pairs of vehicle wheels. A transfer case according to the aforesaid patent and other known automotive transfer cases each utilize a rearwardly extending output or propeller shaft for transmitting torque to the rear wheels of the vehicle.
A typical output or propeller shaft of an automotive transfer case must be capable of accommodating limited axial slip along its longitudinal axis of rotation relative to a coaxial input shaft which transmits torque thereto and/or with respect to a member to which it transmits torque, to accommodate changes in distance that can occur between the transfer case and the rear axle that is driven by the propeller shaft. Such changes can occur as a result of the normal movement of the suspended wheels of the vehicle relative to the body as the vehicle travels over a highway or over unpaved terrain. Thus, such a propeller shaft is normally constructed with an internal spline which receives an end of an output drive shaft from the transfer case and/or with an internal spline which receives an end of a universal joint yoke or other member which is driven by the propeller shaft. In such a splined propeller shaft arrangement, the propeller shaft is encased within an annular housing with a flanged open end which is sealingly secured to the transfer case housing. The housing surrounds the propeller shaft and the end portion of any drive shaft which is received therein in a splined connection, to a location beyond the splined connection between the drive shaft and the propeller shaft. The drive shaft and propeller shaft are each normally rotatingly received in a bushing or rotating bearing, usually an inner bushing at or near the juncture between the transfer case and the housing in the case of the drive shaft and an outer bushing near the outlet of the transfer case in the case of the propeller shaft. In such an arrangement the propeller shaft housing is in fluid communication with the transfer case to permit lubricant from the transfer case to properly lubricate the bushings and other moving parts within the housing.
In a transfer case arrangement as described above, the propeller shaft extends beyond the closed end of the propeller shaft housing to connect with a yoke or other input connection to a universal joint at the differential which serves to drive the rear axle of the vehicle. Where the propeller shaft housing receives lubricant from the transfer case, a suitable seal must be provided between the propeller shaft and the surrounding structure of the opening in the housing through which the propeller shaft extends to prevent lubricant from within the housing from leaking through such opening. Rotating seals which are suitable for such an application are complex and expensive and heretofore it was required that such seals also be able to accommodate axial slip, a factor which further adds to the required complexity of the seal and subjects it to additional life shortening wear. Further, an exposed portion of an oscillating and rotating member can become laden with debris of an abrasive nature, and when such portion moves to a location within a seal, its subsequent rotation can be damaging and life-shortening to the seal.